Online-only scholarship?

On the NPS blog Mysteries and Conundrums, John Hennessy has an interesting post about how far he as a Civil War historian can get today using only online sources. More and more is becoming available, but Hennessy thinks that (at least in his field) we are not yet close to the point where digital collections are all we need:

While it’s astonishing how fast the mass of materials online is growing, we are still far from the day when new, credible, comprehensive, and definitive history can be written from the digital domain alone. Covet your Ipads, but also hang on to those rolls of dimes for the copy machines, continue to make friends in your favorite repositories, and keep those laptops ready for transcription (barbaric though it may seem), because doing really good history requires all those things.

It is difficult to argue seriously with this assessment today, but I cannot help wondering for how long that will be the case.